Internal combustion engine

ABSTRACT

An internal combustion engine in which a stream of air from a duct (46) to a cylinder (2) so as to flow adjacent to the cylinder walls. The duct (46) is arranged to admit the air only while the exhaust valve (42) is open. The air will circulate against the cylinder walls during the exhaust stroke but at least a portion thereof will remain adjacent the cylinder walls during the subsequent compression stroke. The combustible charge is admitted generally centrally of cylinder and remains stratified with respect to the circulating air. The circulating air maintains the combustible mixture relatively concentrated for good ignition, cushions the igniting gases, assists in maintaining the cylinder walls clean and cools the exhaust valve.

This application is a continuation of U.S. application Ser. No. 463,452filed Jan. 21, 1983 now U.S. Pat. No. 4,558,670, corresponding to anationalization of PCT application Ser. No. PCT/AU82/00086 filed May 28,1982, in turn a continuation-in-part of U.S. application Ser. No.202,030 filed Oct. 29, 1980, in turn a divisional of U.S. applicationSer. No. 861,929 filed Dec. 19, 1977, now U.S. Pat. No. 4,249,495.

This invention relates to internal combustion engines, especially, butnot exclusively, to four stroke spark ignition engines.

The U.S. Pat. No. 4,249,495 discloses an internal combustion engine inwhich there are stratified charges of fuel-rich mixture and fuel-leanmixture (or air). The fuel-lean or air mixture is admitted to thecylinder so as to circulate about the cylinder walls and so concentratethe fuel rich mixture in a central core in the combustion chamber. Theair-rich mixture is arranged to remain unmixed with the air so thatconcentrated fuel-rich mixture is located adjacent to the spark plugwhereby reliable ignition takes place.

It has now been found that substantial advantages can be obtained if theair is admitted to the cylinder during the exhaust stroke rather thanduring the induction stroke.

The main advantage to be obtained is that the engine can maintain thecharges stratified even at relatively low throttle settings which is asubstantial advantage since reliable ignition at low throttle settingshas always been a problem with internal combustion engines. Secondly,the circulating air can be used to cool the exhaust valve and thisreduces wear and further reduces the production of oxides of nitrogen.

In this specification, reference is made to the introduction of air tocirculate about the cylinder walls but it is to be understood that anyinert gas could be used. It would be possible to use a lean air-fuelmixture, but air is preferred.

According to the present invention there is provided an internalcombustion engine comprising at least one cylinder, a pistonreciprocally mounted in the cylinder, a cylinder head having acombustion chamber formed therein, an inlet port for admission ofair-fuel mixture, an exhaust port for egression of combustion products,inlet valve means for opening and closing said inlet port, an exhaustvalve means for opening and closing said exhaust port, timing means forcontrolling said inlet and exhaust valve means, characterized by theprovision of air inlet means for admitting a tangential stream of airadjacent to the cylinder when said exhaust valve means is open.

The invention also provides a cylinder head for an internal combustionengine, said engine having at least one cylinder and a pistonreciprocally mounted in the cylinder, said head having a combustionchamber formed therein, an inlet port for admission of air-fuel mixture,an exhaust port for egression of combustion products, an inlet valve foropening and closing said inlet port, an exhaust valve for opening andclosing said exhaust port, timing means for controlling said inlet andexhaust ports, characterized by the provision of air inlet means foradmitting a tangential stream of air adjacent to the side walls of thecombustion chamber when said exhaust valve is open.

The invention will now be further described with reference to theaccompanying drawings, in which:

FIG. 1 is an axial cross section through a four stroke engine embodyingthe invention,

FIG. 2 is a cross sectional view taken along the line 2--2,

FIG. 3 is a top plan view of the arrangement shown in FIG. 1,

FIG. 4 is a view into the combustion chamber of the arrangement shown inFIG. 1,

FIG. 5 is a view looking into the head from beneath a modifiedarrangement of the invention, and

FIG. 6 is a schematic axial cross-section through a two valve fourstroke engine having air inlet ducts formed in the cylinder wall.

FIGS. 1 to 4 illustrate one cylinder of a four stroke engine which mayhave in practice included any number of identical cylinders. The engineincludes a cylinder block 1 formed with a cylinder 2 within which apiston (not shown) is reciprocally mounted. A cylinder head 3 is mountedon top of the cylinder block and includes inlet and exhaust ports 8 and40 for each cylinder. Inlet and exhaust valves 10 and 42 are providedfor opening and closing the ports 8 and 40 and timing means (not shown)of conventional construction can be provided for opening the valves inthe correct sequence.

The inlet port 8 is connected to a carburettor (not shown) in the usualmanner and is directed so as to introduce air-fuel mixture into thecylinder 2 generally centrally thereof and without any substantialtangential component. A spark plug 43 is located generally centrally ofa combustion chamber 5 formed in the head.

The head includes an inlet pipe 46 for admission of a non combustiblegas such as air so as to swirl adjacent to the cylinder wall. The end ofthe pipe 46 is located near the cylinder wall so that air is dischargedtherefrom with a substantial downward and tangential component so thatthe air will swirl about the inner walls of the cylinder. The pipe 46 ispreferably connected to a blower (now shown) which supplies air theretoat about 10 p.s.i. The blower can remain in continuous operation so thatit will circulate cool air over the back of the exhaust valve 42 whenthe latter is closed. This is particularly useful since it cools theexhaust valve and this has the effect of reducing the production ofpollutants, notably oxides of nitrogen. Further, it also reduces wear onthe exhaust valve.

In a normal four stroke engine, the timing is arranged so as to operatethe exhaust valve 42 and open the port 40 when the piston is near bottomdead centre. At this point the exhaust gases within the piston are at arelatively high pressure and are rapidly expelled from the port 40. Atthis stage, the flow of air from the pipe 46 may cease because of therelatively high pressure but this is only a temporary condition sincethe pressure will soon fall to atmospheric or even below atmosphericbecause of the kinetic effect of the discharging exhaust gases. Once thepressure has dropped to about the same level as that applied to the pipe46 by the blower, cold air will be admitted into the cylinder so as toswirl about the cylinder wall. The swirling mass of relatively cold airhas a number of beneficial effects. Firstly, the air will tend to coolthe cylinder walls and so reduce heat losses through the cylinder wallsand reduce wear on the cylinder walls. Second, as the piston proceedsthrough the exhaust stroke, the circulating air will tend to force theresidual exhaust in the head space out the exhaust port 40 and so havean important scavenging effect. Third, and most importantly, when theexhaust valve closes there will be remaining in the head space acirculating stream of relatively cool air which will tend to remaincirculating within the combustion chamber even when the new charge ofair-fuel is admitted after opening the inlet valve 10. The air-fuel thusresides in a central core in the cylinder with the relatively cool aircirculating about the cylinder walls and this situation tends to remainunchanged during the induction stroke and the subsequent compressionstroke. Therefore, at the time of firing of the spark plug 43, theair-fuel mixture is located in a central core immediately adjacent tothe spark plug 43, with the cool air still circulating about thecombustion chamber 5.

In order to enhance the effect of stratification of charges as notedabove, it is desirable that the combustion chamber 5 be formed as asurface of revolution with a minimum of projections therein. Further,the bottom of the valves 42 and 10 lie flush with the upper part of thecombustion chamber when closed. The stratification effect just describedwould be further enhanced by locating the inlet port 8 more centrally ofthe head and by heating the air-fuel mixture prior to admission so as toreduce its effective density.

It will be appreciated that the air-fuel mixture will tend to beconcentrated in a core near the spark plug 43 so that reliable ignitionoccurs. This will be the case even though there is an overall air-fuelratio which is much less than stoichiometric because of the air admittedthrough the pipe 46. A further advantage is that once ignition doesoccur, the circulating air located near the cylinder wall has acushioning effect and so reduces the tendency for peaks of pressure tooccur in the cylinder. In view of the latter effect, it is envisagedthat non-leaded fuels could be utilised in engines of the invention.

The arrangement of FIG. 5 is essentially the same as that shown in FIGS.1 to 4 except that in this case the cylinder head 3 is provided with asecond air inlet tube 47 which opens to the inlet port 8 instead of theexhaust port. The pipe 47 is directed tangentially and downwardly as isthe pipe 46 and the air admitted there through tends to assist inmaintaining the centrificial stratification of charges during theinduction stroke of the engine since the pipe 47 will admit air to thecylinder when the inlet valve 10 is open.

FIG. 6 illustrates an alternative arrangement in which air is admittedto the cylinder at or near the bottom of the exhaust stroke of thepiston 6. Air is admitted through ports 58 in the cylinder whichregister with ducts 60 which are provided with valves 62 synchronisedwith the timing of the exhaust and inlet valves 42 and 10. The airadmitted at the bottom of the stroke could be an alternative to thearrangement shown in FIG. 1 or additional thereto.

It is preferred of course that the tubes 62 be disposed so as to imparta tangential component to the incoming air so that it will circulateagainst the cylinder wall. Further, the air should have an upwardcomponent of velocity and this can be effected by means of a deflectingrebate 30 provided near the crown on the piston, as seen on theleft-hand side of FIG. 6. On the right-hand side, there is shown avariation where the ports 58 register with ducts 64 formed into thepiston crown, the orientation of the ducts 64 being chosen to impart atangential and upward component of velicity to the incoming air.

The invention is also applicable to two stroke engines. In particular,it would be applicable to two stroke engines which include an inletvalve in the head for admission of combustible mixture to the cylinderand arrange to have exhaust ports in the bottom of the cylinder wall,these ports being opened when the piston is near bottom dead centre ofits stroke. The tangential air would be admitted through the exhaustports or adjacent thereto and operate to introduce circulating airaround the cylinder walls and such circulating air would tend to assistin scavenging the exhaust from the cylinder.

The invention is also applicable to diesel engines. For instance, asuitable arrangement would be similar to FIG. 1 except that the sparkplug 43 would be replaced by a fuel injector arranged to direct fuelcentrally of the cylinder and air (or other working fluid) would beadmitted through the inlet port 8 under control of the inlet valve 10.

The air or relatively inert gas admitted through the pipe 46 also servesto keep the fuel rich mixture away from the cylinder walls. This wouldbe especially important where solid hydrocarbons, such as coal dust,were mixed with the liquid fuel charge, the latter technique beingpresently investigated with injected diesel engines.

In the arrangement illustrated in FIG. 1, it may in some circumstancesbe desirable to include a flap valve (not shown) in the pipe 46 so as tostop the high pressure exhaust gases entering the blower. Alternatively,the end of the pipe 46 in the exhaust duct may be so shaped so as toavoid admission of exhaust gases in the pipe 46. One such shape isillustrated in FIG. 3 where the end of the pipe 46 is shown as having anangular end 80 (shown in chain line in FIG. 3), the angular end havingits longer face upstream of the exhaust flow.

A further advantage of the invention is that the introduction of airinto the exhaust tends to dilute the exhaust gases.

In the arrangement illustrated in FIG. 5, it would be possible toarrange for the pipe 47 to receive its air from the atmosphere oralternatively to be connected to the same blower which supplies airunder pressure to the pipe 46. The pipe 47 may include its own valvewhich is synchronised with the inlet valve 10 or alternatively mayutilise the valve 10 itself to control admission of air into the piston.Similarly, the pipe 46 may include a separate valve for controllingadmission of air to the cylinder. If separate valves are provided forthe pipes 46 and 47, these can be timed from the cam shaft which wouldnormally be provided for operating the valves 10 and 42.

Many modifications will be apparent to those skilled in the art withoutdeparting from the spirit and scope of the invention.

I claim:
 1. A method of operating an internal combustion engine having acylinder and piston reciprocally mounted therein, said method includingegressing combustion products from the cylinder during an exhauststroke, admitting to the cylinder a tangential stream of air only duringsaid exhaust stroke at a pressure and direction relative to the cylindersuch that said stream of air circulates against the cylinder wall,introducing a combustible mixture of a working fluid and fuel into saidcylinder during an induction stroke, maintaining said stream of air andsaid combustible mixture substantially stratified during a compressionstroke, in which the engine includes an exhaust duct and an exhaustvalve for opening and closing same to said cylinder and in which thestep of admitting to the cylinder a tangential stream of air includesrouting the air stream through an opening, as seen in plan, transverselyinto said exhaust duct adjacent to and generally tangentially of saidcylinder wall, and avoiding exhaust flow into said opening when saidexhaust valve is open by providing the opening with a shielding meansupstream in the exhaust flow from said opening.
 2. A method of operatingan internal combustion engine having a cylinder and piston reciprocallymounted therein, said method including egressing combustion productsfrom the cylinder during an exhaust stroke, admitting to the cylinder atangential stream of air only during said exhaust stroke at a pressureand direction relative to the cylinder such that the stream of aircirculates against the cylinder wall, introducing a working fluid intosaid cylinder, maintaining said stream of air circulating about thecylinder wall during a compression stroke of the engine and injectingfuel centrally of the cylinder into said working fluid, whilstmaintaining stream of air stratified with respect to said working fluid,in which the engine includes an exhaust duct and an exhaust valve foropening and closing same to said cylinder and in which the step ofadmitting to the cylinder a tangential stream of air includes routingthe air stream through an opening, as seen in plan, transversely intosaid exhaust duct adjacent to and generally tangentially of saidcylinder wall, and avoiding exhaust flow into said opening when saidexhaust valve is open by providing the opening with a shielding meansupstream in the exhaust flow from said opening.
 3. A method as claimedin claim 1, wherein said engine includes an exhaust port and whereinsaid stream of air is admitted to the cylinder through the exhaust portsuch that it cools said exhaust valve.
 4. A method as claimed in claim1, wherein two of said tangential streams of air are admitted atopposite sides of the cylinder to circulate against the cylinder wall inthe same direction.
 5. A method as claimed in claim 1, wherein thecombustible mixture is heated prior to admission to the cylinder so asto enhance stratification relative to said stream of air.
 6. A method asclaimed in claim 1, wherein a further stream of air is admitted throughan opening in the cylinder wall at or near the bottom of the stroke ofthe piston.
 7. A method as claimed in claim 6, including the step ofimparting an upward component of velocity to said further stream of airby means of at least one formation on the piston.
 8. A method as claimedin claim 3, wherein two of said tangential streams of air are admittedat opposite sides of the cylinder to circulate against the cylinder wallin the same direction.